The present invention relates to a method for operating a gear grinding machine. Such gear grinding machines are used for machining a workpiece on the gear grinding machine by means of a grinding disk and/or grinding worm.
In the production of gear wheels, gear grinding machines are used for hard finishing premachined gear wheels, in order to provide them with their final geometry. In the production of gear wheels, teeth usually are first formed from a rotationally symmetric workpiece in a soft premachining step, e.g. by milling or slotting. Then, the workpiece premachined in this way is subjected to a heat treatment, by means of which at least the regions of the gear wheel located near the surface of the teeth are hardened. To compensate the changes in the surface geometry which occur during the heat treatment and to fabricate the surface geometry of the teeth with greater precision, hard finishing is performed on the gear grinding machine. There is used a grinding disk or a grinding worm, with which the workpiece is machined and which provides the same with its final geometry.
Such gear grinding machine is shown in FIG. 1. The same includes a workpiece fixture 3, in which a workpiece 6 can be clamped. The workpiece fixture 3 is rotatable about the axis C2, which advantageously is vertically aligned. Alternatively, however, horizontally aligned workpiece fixtures can also be used. The gear grinding machine furthermore includes a work spindle 5 for clamping a tool. One or more grinding disks and/or one or more grinding worms 1 can be clamped into this work spindle 5. The work spindle 5 can be rotated by the motor 8, wherein the axis of rotation B1 of the work spindle 5 can be swivelled in a plane which extends parallel to the axis of rotation of the workpiece fixture 3. For this purpose, the work spindle 5 can be swivelled about a swivel axis A1, which is vertical to the plane in which the axis of rotation B1 of the work spindle 5 extends, and which also extends vertical to the axis of rotation of the workpiece fixture 3. Furthermore, the work spindle 5 can be shifted linearly in the direction of its axis of rotation B1, i.e. along the arrow V1. Furthermore, the work spindle 5 can be moved linearly in a direction parallel to the axis of rotation C2 of the work spindle 5, i.e. along the arrow Z1. The work spindle also can be moved linearly in a direction vertical to the axis of rotation C2 of the workpiece fixture 3, i.e. along the arrow X1, in order to move the grinding disk or grinding worm 1 clamped into the work spindle 5 towards the workpiece clamped into the workpiece fixture 3 or to move it away from the same or to achieve specific corrections. Machining the workpiece with the grinding disk or grinding worm usually is effected by generation grinding or profile grinding or a combination thereof.
The developments made in gearbox construction for transmitting higher power densities with lower noise emission lead to increasingly complex gear geometries or gear topologies of gear wheels. Owing to this modification of the gear geometries, the gear-tooth contact patterns can be optimized under various load conditions, and the thrust and tensile loads between the meshing teeth can be improved. There is a trend towards increasingly complex gear wheel geometries, which must be produced in shorter and shorter reaction times in smaller batch sizes.
To adapt the grinding disks or grinding worms to the desired geometry of the gear wheel and/or to compensate the wear of a grinding disk and/or grinding worm, the grinding disk or grinding worm must be dressed in regular intervals during operation for adjustment to a new geometry of the workpiece. Dressing or trueing a grinding disk and/or grinding worm comprises the actual profiling, i.e. generating the required geometry of the grinding disk and/or grinding worm (concentricity, cylindricity, profile), and sharpening, i.e. generating a high-cutting grinding surface (microgeometry), and subsequently continuously is referred to as profiling for reasons of clarity. Subsequently, the tool used for profiling a grinding disk or grinding worm correspondingly is referred to as profiling tool.
For profiling grinding disks and grinding worms, in particular cylindrical uncorrected grinding worms and cylindrical modified grinding worms, different profiling tools are used. FIGS. 2 to 4 show such profiling tools 2, which are used for profiling a grinding worm 1. In FIG. 2, rotationally symmetric profiling tools are shown, and in FIG. 3 a profiling tool in the form of a gear wheel which also is referred to as profiling gear (master gear). FIG. 4 shows further rotationally symmetric profiling tools with more complex geometries.
Profiling the grinding disks or grinding worms can be effected on the gear grinding machine, i.e. on the production machine, on which the gear wheels also are machined. For this purpose, the profiling tools on the gear grinding machine, as shown in FIG. 1, are mounted on a profiling spindle, are driven by the same and, if necessary, can selectively be swivelled about their clamping axis. The profiling spindle 4 of FIG. 1 can be driven about the axis of rotation B3, which extends vertical to the axis of rotation C2 of the workpiece fixture. In addition, the profiling spindle 4 can be swivelled about the swivel axis C5, which extends parallel to the axis of rotation C2 of the workpiece fixture 3. Furthermore, the profiling spindle 4 is linearly movable in a direction which extends parallel to the axis of rotation C2 of the workpiece fixture 3, i.e. along the arrow Z4. During profiling, the grinding disk or grinding worm to be profiled likewise is driven and selectively swivelled towards the profiling tool, so that profiling the grinding worm can be effected in normal cut. Profiling the grinding worm is performed either single-flank or dual-flank in several passes, and if necessary the profile flanks can be profiled in different ways and variable along the worm length, in order to produce a so-called three-dimensionally modified grinding worm.
The grinding disks or grinding worms for grinding the workpiece usually are made of bound hard material grain, e.g. corundum or a corundum modification, or of ceramically bound or galvanically bound boron nitride. The accuracy of the profiling of the grinding disk or grinding worm determines the accuracy of the gear teeth to a large extent. The profiling tools used in the prior art usually are coated with a single layer of hard material and preferably are galvanically positively or galvanically negatively coated with diamond or cubic boron nitride and also are subsequently conditioned mechanically, in order to meet the required high final quality in terms of profile geometry and tool life. Manufacture usually requires a basic metallic body, which likewise must be manufactured mechanically in close quality, a chemical or electrochemical coating process and, if necessary, an accurate mechanical finishing, i.e. profiling or dressing the profiling tool. Trueing or dressing a profiling tool, which in turn comprises the actual profiling, i.e. generating the required geometry of the profiling tool (concentricity, cylindricity, profile), and sharpening, i.e. generating a high-cutting profiling surface (microgeometry), subsequently continuously is referred to as dressing, in order to avoid confusions with the profiling of a grinding disk and/or grinding worm. The tool used for dressing a profiling tool likewise continuously is referred to as dressing tool.
The process for manufacturing known profiling tools is a multistage and time-consuming process, the tool produced has a predefined geometry, which must accurately be matched between the tool supplier and the customer and should be preserved over a long service life. Manufacture is ensured by a small number of specialized tool manufacturers worldwide. Due to the specific procedure, the tools are relatively expensive and have considerable terms of delivery. For dressing or recoating and dressing, the tools must be sent back to the manufacturer and a so-called recoating or resharpening process is started. In such process, changes in the geometry of the profiling tools can also be performed within certain limits at certain costs.
The disadvantages of the tool systems available so far consist in that changes in the profile geometry of the customer workpiece, which cannot be accomplished by swivelling or by selective feeding when dressing the grinding worm, only can be produced by so-called line dressing. However, this method involves the disadvantage that the line-shaped pre-, finish- and postprofiling of a cylindrical grinding worm is very time-consuming due to the multitude of individual profiling steps and therefore is only partly suitable for grinding recurring batch sizes on the production machine.